A 99.8% confidence interval for the average weight of a box of
cereal if a sample of 24 such boxes has an average of 18.08 ounces
with a sample deviation of 0.235 ounces. The population of all such
weights is normally distributed
round to the nearest hundreth of an ounce
X_bar =18.08
= 0.235
n=24
Df = n-1 = 24-1 =23
Now calculate 99.8% confidence interval is given by formula
CI = x_bar t*(/n)
t value for 99.8 confidence interval is with df =23 is 3.485
t = 3.485
CI = 18.08 3.485 *(0.235/24)
= 18.08 0.167
CI = 18.08 - 0.167 and CI = 18.08 + 0.167
= 17.913 CI = 18.247
Therefore 99.8% confidence interval is (17.913,18.247).
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